1. Field of the Invention
The invention relates generally to alignment devices used in the assembly of mechanical components such as engine parts, and more particularly to locating implements used in aligning an engine head on an engine cylinder during assembly or reassembly.
2. Description of the Related Art
Small internal combustion engines are used in a wide variety of applications. One example of such engines has been manufactured by the Yamaha Corporation of Japan for 20 years or more. It is a single cylinder, air-cooled, two-cycle engine, which is widely used in go-cart racing, among other activities.
The engine is air-cooled by way of cooling fins on both the cylinder and the head. The head, mounting a spark plug, is removably attached to the block, which is in turn coupled to or integral with the case. The block contains a cylinder lined with a cylinder sleeve in which a piston is located, connected in conventional fashion to a crank shaft in the case.
The head has a recessed combustion chamber which must be centered over the cylinder in order to achieve maximum performance. This recessed portion, or dome, must be symmetrically positioned relative to the piston and cylinder or the burn pattern will be uneven and will result in lost performance.
As previously mentioned, these small internal combustion engines are often used in the highly competitive sport of go-cart racing. Racing classifications impose restrictions on several aspects of engine design, including displacement as well as other dimensions and parameters. In the course of a typical race day, the head may be removed from the cylinder four or five times in order to permit maintenance and repairs, as well as to accommodate inspections by race officials and others.
As mentioned above, accurate positioning of the recessed portion, or dome, relative to the piston in the cylinder is essential to achieve peak performance from the engine. The head is secured to the cylinder by nuts threaded onto six studs extending from the cylinder and passing through the head. The studs are evenly spaced in a symmetrical pattern, centrally aligned with the cylinder. The head is designed with stud-receiving holes adapted to receive the studs extending from the cylinder. With these engines as heretofore constructed, it is no simple task to achieve the desired alignment of the head on the cylinder. The problem stems from the excessive tolerance in the dimensions of the stud holes in the head relative to the studs which must extend therethrough to receive the nuts which, when tightened down, fix the head in place on the cylinder.
The studs are nominally 8 mm in diameter, and as a result of manufacturing considerations, the inside diameter of each stud-receiving hole of the head is approximately 1/16" larger than the outside diameter of the studs. The reason for the allowance of this spacing between the hole diameter and the stud diameter is to provide simplification of the manufacturing process. One engine manufacturer, the Yamaha Corporation of Japan, produces several combinations of heads and blocks which permit interchangeable use but necessitate this greater spacing. This spacing between stud and stud holes creates variability in engine performance depending upon accuracy of assembly. More specifically, maximum performance can only be obtained when the engine is assembled such that the head, and therefore the dome, is accurately positioned and centered over the piston and cylinder.
The procedure commonly used for centering the dome over the piston typically takes between 15 and 20 minutes to complete, and involves the repetition of a particular positioning procedure in order to ensure accurate assembly. This positioning procedure employs a length of soft solder, which is then bent and inserted through the spark plug hole in the top of the head and extended to the outer edge of the combustion chamber. The piston is then rolled through its top dead center position in order to create an impression upon the solder. The impression records the area of overlap between the face of the piston and the flat portion of the head surrounding the dome. This overlap area is commonly referred to as the "squish area" and the procedure as the "squish test". The solder is then removed and the squish area inspected to determine if the head is accurately and symmetrically positioned over the cylinder. If the position of the head is not satisfactory, i.e. the squish area is not uniformly distributed around the cylinder perimeter, the head is repositioned slightly and the squish test is repeated.